Rust problem on unusual exterior window frame

[Nigel Watts]

I have a bespoke steel and glass bay window on the modern extension. It was made by a metalworker to a non-standard design and is now suffering from a rust problem.

The double glazed window units are held in an L-section steel frame with mastic. These L-section frames are only attached to the structural steelwork in a few places and a gap about 3/8 to 1/2 inches wide was left between the L-section frame and the structural steelwork. The gap in the steelwork was then filled with mastic. Water has now penetrated between the mastic and the steel causing, in some place, very bad rusting.

The first pic shows the symptoms before I removed the mastic (the top join has failed but the lower one is still in reasonable nick):

The next pic shows what it looks like after mastic removal:

How should I repair this? I could try to remove all the rust (difficult given the narrowness and depth of the gap), repaint and then remastic. A more radical, and probably better solution might be to get a welder in to weld the gap. This would almost certainly crack the glass however, although some of it needs replacing anyway.

Ideas would be appreciated.

 

[88v8]

Well, that's a cockamany design. What genius dreamed that up. Might have lasted a while if everything had been hot-dip galvanised.
As you say, no chance whatever of welding it.

So... are you bodging this up to sell the place?
Or do you want a lasting solution?

The best solution of course would be to remove the whole steelwork and redo it in brass.
Or galvanised. But one can't weld galvanised after galvanising.
How is the L shape sealed against the glass?

Anyway, it seems the problem is that the water has got behind, and one can't get at behind.
If I were stuck with it, I'd get someone to come and sandblast the steelwork including the joint space.
Then treat it with Jenolite sprayed in.
Then spray it with this
http://www.rust.co.uk/epoxy-mastic-rust-proofing-paint/c28117/

it will have be to be sprayed to get into the space, and it's a two-pack so there's a pita straight away, but it is verrrrrry durable.**

Then I'd refill the mastic space with Arbo 1096.
http://www.arbo.co.uk/arbo-sealants/arbosil-1096/
Like any decent highly elastic sealant, one can't overpaint.

Not a job I'd want to do at all at all. I hate trying to fix things that I know will not endure.
I'd enjoy much more putting the whole lot in a skip.

Ivor

** the finish is satin, but with uv softens in tone to something akin to lead paint.

 

[Nigel Watts]

Thanks Ivor

I intend living in my house for some time so I don't really want to do just a bodge job. Our architects specified the steelwork but the builder's bother (the metalworker) built it differently, hence the problem it would seem. The architect had also specified an epoxy paint but I suspect the builder had not used it properly and my guess is that he did the mastic filling before he had properly coated the steelwork. I was wondering if I could get a narrow wire brush into the gap to get rid of the rust or perhaps use a chemical rust remover.

Nigel

 

[Moo]

Possibly a very silly question, Nigel, but what does your builder say?

 

[88v8]

Oops

 

[88v8]

Thanks Ivor
I intend living in my house for some time so I don't really want to do just a bodge job. Our architects specified the steelwork but the builder's brother (the metalworker) built it differently, hence the problem it would seem. The architect had also specified an epoxy paint but I suspect the builder had not used it properly and my guess is that he did the mastic filling before he had properly coated the steelwork. I was wondering if I could get a narrow wire brush into the gap to get rid of the rust or perhaps use a chemical rust remover.
Nigel

Ahhh, well-meaning relatives. I've had some of that. All quality control goes out of the window.

Wire brush - if the gap is sufficiently wide, probably the most effective means would be a Dremel, for which one can purchase a variety of wire brushes.
http://www.ebay.co.uk/bhp/dremel-wire-brush

Having removed as much surface rust as possible, the Jenolite is a chemical rust convertor, so that will do the job of inerting the rust, insofar as one can get at the surface.

The problem is that the rust will have crept behind the accessible faces, whence it will eventually permeate beneath the new coating. Indeed, the fact that it is rusting at the bottom suggests that the joint between the glass and the metal has failed, so water is sitting behind.
I fear that whatever you do, in a few years it will need to be done again.

I suppose there are two issues really with the rust, one the cosmetics and the other the structure. You could just affix a cosmetic cover over the metal work, copper for instance, then the rust will not be visible.
Eventually, it will get so bad that it will crack the glass, and in the longer term it will begin to collapse but this could be many many years away. In the meantime you can just give it a good ignoring.

At some point your sealed units will mist and need replacing. Perhaps that would be a logical point at which to bite the bullet, pull it all out and remake with brass sections, which should be at least an eighth thick. They can be brazed or mechanically fastened. Then there will be no more corrosion problem.
I had some brass dg made for our previous house in U channel, albeit smaller sizes. Main problem is ensuring that it's kept flat and the inner surfaces free of brazing blob, but a good metalworker can accomplish this. Then a suitable sealant such as Arbo
http://www.arbo.co.uk/arbo-sealants/arboflex-500/
is required between frame and glazing, but I would talk to Arbo about this before making a selection.

Do not at any point allow your builder to choose sealants or you are liable to end up with any old thing.
Arbo products are not available from your local DIY or Builders merchants, they have to be ordered, worthwhile as they are very good.

Or perhaps instead of brass, some aluminium or proprietary metal glazing system (says he vaguely) which would have the merit that you are buying someone else's tested product, instead of another leap in the dark.
Or could have the merit, depending who installs it. There is no system so wonderful that it cannot be fouled up on site.

All very annoying.

Good point that Moo makes.

Ivor

 

[Nigel Watts]

I have decided to asked the architect. No reply so far.

 

[malcolm]

It should have been galvanised to start with. Now you are where you are I'd try cleaning the rust out as best as possible with sand paper down the gap (or better get a sand blaster in).

Bilt Hamber do a 95% zinc paint which really does give galv protection. Sticks poorly so needs a blasted or really well sanded surface. After that use polyurethane sealer from a car paint shop. 2 pack paint on top is weatherproof and flexible and not too bad for health when brushed but still needs a carbon mask.

Think car not buildings. Old cars are also built from the wrong material but my 60 year old still enjoys a run in the sunshine.